Prosthetic heart valves are used to replace damaged or diseased heart valves. Prosthetic heart valves for human patients have been available since the 1950s. Today, there are three general types of prosthetic heart valves, including mechanical valves, tissue valves, and polymer valves. In some cases, a heart valve prosthesis is implanted into an annular opening in a patient's heart following surgical removal of a diseased or damaged natural valve. The valve can be secured in the annulus of the opening through the use of sutures or pins that penetrate the host tissue and an outside edge of the valve. Alternatively, the valve can be secured in the annulus by suturing the host tissue to a sewing ring. Heart valves function essentially as one-way check valves for blood flow through the beating heart.
The term “mechanical valve” refers to mono- or multi-leaflet (typically bi-leaflet) heart valves having a valve orifice fabricated at least in part of a rigid, biologically compatible material such as pyrolytic carbon, and comprising essentially no biological components. The term “bioprosthetic valve” refers to a multi-leaflet (e.g., bi-leaflet or tri-leaflet) heart valve having at least some biological components such as tissue or tissue components. The biological components of tissue valves are obtained from a donor animal (typically bovine or porcine), and the valve may comprise either biological materials alone or biological materials with man-made supports or stents. The term “polymeric valve” refers to a multi-leaflet (e.g., tri-leaflet or bi-leaflet) heart valve having at least some elastomeric polymer components, including at least elastomeric polymer valve leaflets.
A tri-leaflet heart valve prosthesis typically includes an annular valve body and three flexible leaflets attached thereto. The valve body includes an annular base and three leaflet support posts located at the circumference of the annulus. In some cases, a sewing ring annularly coupled to the periphery of the valve body may provide a place for sutures to be applied when the valve is implanted. The leaflets are attached to the three shaped posts along an attachment curve, and they also each have a free, unattached edge remote from the attachment curve. The place where two adjacent leaflets come together at one of the support posts is called the commissure, and the generally curved area on the leaflet between the free edge and the attachment curve is known as the belly of the leaflet. The free edges of the three leaflets come together at a “triple point” generally on the axis of the valve.
When blood flows in the forward direction, the energy of the blood flow deflects the three leaflets away from the center of the annulus and allows blood to flow through. When blood flows in the reverse direction, the three leaflets engage each other in a coaptive region, occlude the valve body annulus and prevent the flow of blood.
Heart valves may be may be implanted through open heart surgical procedures. More recently, heart valves have been developed that are implanted percutaneously, e.g., using transcatheter procedures. Transcatheter percutaneous aortic replacement valve devices typically include a valve body mounted on a tubular expandable (e.g. balloon expandable or self-expanding) stent or frame. Examples include the SAPIEN device available from Edwards Lifesciences of Irvine, Calif. or the CoreValve device available from Medtronic of Minneapolis, Minn.
Percutaneously implanted devices obviate the need for major open surgical procedures. However, implantation of these devices may be difficult. Replacement valves are typically sensitive devices, and care must be taken to avoid damage during implantation. In the case of aortic replacement valves, further difficulties may arise from the particular anatomy of the aortic region. The aortic region is characterized by high blood pressure subjecting tissue is in the area to high physical strains. Supporting stents for aortic replacement valves therefore must sufficiently be robust and rigid to operate in this environment. However, the introduction of such a stent in the region raises the risk that other vessels, such as the coronary arteries ostium dextra and ostium sinistra (referred to herein as the coronary ostia) descending on both sides of the aorta, may be disrupted in their function.